(1) Field of the Invention
This invention relates to an inkjet printer and a maintenance method thereof. It specially relates to a technique of discharging air accumulated in supplying paths of ink and to a cleaning technique of a printing head.
(2) Background Art
Various inkjet printers which can print texts and images with plural colors of ink supplied from ink cartridges of plural colors have been used.
In order to give positive pressure to ink, some types of ink cartridges, wherein ink is supplied through tubes, are constituted to reserve ink in bags made of thin films in ink reservoirs, to have air chambers outside of the bags and to supply pressurized air into the air chambers.
An air supply system which generates this pressurized air has an air pump, a drive motor which drives the air pump, an air tube extending from the air pump, plural branched-paths branched from the air tube to plural ink cartridges and a pressure regulator, a relief valve or an orifice connected to the air tube in the vicinity of the air pump for pressure adjustment.
For example, Sato et al (Japanese Patent No. 2703647) discloses an inkjet printer comprising such an air supply system described as above constituted with a relief valve for pressure adjustment an air temperature sensor which detects air temperature and a pressure sensor which detects pressure of pressurized air in an air tube. It discloses an art to correct driving voltage for driving a pump driving motor according to air temperature detected by the air temperature sensor when pressurized air is to be generated before or after an usage of the printer.
Kumagai (Unexamined Japanese Patent Publication No. 10-138506) discloses an inkjet recording apparatus comprising an air supply system described as above having a pressure regulator and changeover valves inserted in branched-paths disposed therein.
These kinds of air supply systems have been used to vacuum ink from nozzles to clean nozzles of printing heads. In other words, these kinds of air supply systems have been used to facilitate ink vacuum by increasing pressure on ink when au ink vacuum from nozzles is conducted.
However, if the pressure on ink applied with these kinds of air supply systems is too high when an ink vacuum from nozzles of an inkjet printer is conducted, ink leaks unnecessarily. If the pressure is too low, on the other hand, ink vacuum cannot be sufficiently conducted.
These air supply systems described above can be also used to discharge air accumulated in ink supply paths. Accumulated air can be discharged by opening some parts of the ink supply paths temporary while the ink supply paths are pressurized by the air supply system.
However, if the pressure on the ink supply paths applied by the air supply system is not enough to discharge air accumulated in the ink supply paths, air cannot be discharged sufficiently. Moreover, it takes longer to discharge air. On the other hand, if the pressure of pressurized air is too high, ink leaks unnecessarily from an air vent, and noise generated by the air supply system becomes louder.
Generally, appropriate air pressure applied to vacuum ink is mainly to prevent a destruction of a meniscus when a vacuum cap is removed from a head, and is lower than appropriate air pressure for an air discharge from ink supply paths. If air pressure generated by an air supply system is set appropriately for an ink vacuum, the air pressure is not enough for an air discharge and air cannot be discharged sufficiently. Contrary, if air pressure generated by an air supply system is set appropriately for an air discharge, the air pressure becomes so high that it causes an unnecessary ink leakage when ink is vacuumed.
Moreover, the pressure of pressurized air generated by the air supply system and flow rate thereof, vary depending on environmental temperature and variations in characteristics of air pumps constituting the air supply systems. These variations sometimes cause problems described above when an ink vacuum and an air discharge from ink supply paths are conducted.
This invention was made in consideration of above described issues, and one of its purposes is to provide an inkjet printer wherein unnecessary ink leakage does not occur when an ink vacuum from nozzles of a printing head and a discharge of air accumulated in ink supply paths are conducted, wherein an ink vacuum and an air discharge can be sufficiently conducted, and wherein noise generated by an air supply system is reduced, and to provide a maintenance method of such inkjet printer.